1. Field of the Invention
The present invention relates to a semiconductor element mounting method and a semiconductor device and, more particularly, to a flip-chip mounting method for mounting a semiconductor element on a substrate and the device formed thereby.
2. Description of the Related Art
Recently, with miniaturization and price reduction of electronic equipment, structures for mounting a semiconductor element on a substrate at a high density have been simplified. One method that has been employed is a so-called "flip-chip mounting method" as a semiconductor element high-density mounting structure having such a simplified structure.
In the flip-chip mounting method which is disclosed, for example, in Japanese Unexamined Patent Publication No. Hei. 4-82241, a semiconductor element is mounted with a plurality of bump electrodes on at least one of its surfaces, and is connected to a circuit board with the surface (e.g., having the bump electrodes) placed downwardly.
A conventional flip-chip mounting structure will be described with reference to FIGS. 5(a) and 5(b), which illustrate the same structure disclosed in FIGS. 1A and 1C of JPA 4-82241.
An insulative resin layer 32 made of a material capable of elastic recovery, such as rubber, is formed on a circuit board 31. Mounting pads 33 also are formed on the insulative resin layer 32 by sputtering or evaporation. A sealing resin 35 is applied to a region of the insulative resin layer 32 through which a semiconductor element 34 is to be fixed to the board 31. A plurality of bump electrodes 36 are formed on a surface of the semiconductor element 34 on the board 31 side.
The plurality of bump electrodes 36 provided on the bottom surface of the semiconductor element 34 are aligned with the mounting pads 33 on the board 31. Then, the semiconductor element 34 is brought into pressurized contact with the board 31 (e.g., element 34 and board 31 are pressed together), whereupon the sealing resin 35 between the bump electrodes 36 of the semiconductor element 34 and the mounting pads 33 on the board 31 is squeezed outwardly (e.g., extruded). The sealing resin extrusion causes the bump electrodes 36 and the mounting pads 33 to become connected together electrically.
In the conventional flip-chip mounting structure illustrated in FIGS. 5(a) and 5(b), the electrical connection between the bump electrodes 36 and the mounting pads 33 is maintained stably due to the elastic recovery property (force) of the insulative resin layer 32 and the contraction force of the sealing resin 35.
However, in the conventional flip-chip mounting structure, the elastic recovery force of the insulative resin layer and the contraction force of the sealing resin weaken over time, as shown in a time acceleration test, such as a temperature cycle test. This is a problem.
Specifically, sometimes the thermal expansion may exceed the contraction force and the elastic recovery force of the insulative resin layer, so that openings or gaps are formed between the bump electrodes and the mounting pads. These gaps may cause a connection failure between the semiconductor element and the board. This produces defective devices, which results in costly and time-consuming repairs and/or waste.
Further, in the above conventional flip-chip mounting structure, when the semiconductor element 34 is connected to the board 31, the mounting pads 33 and the insulative resin layer 32 are sometimes elastically deformed. When the balance between the contraction force of the sealing resin 35 and the elastic recovery force of the insulative resin layer 32 changes due to temperature variation (e.g., the contraction force of the sealing resin 35 becomes greater or less than the elastic recovery force of layer 32), the deformation state of the mounting pads changes accordingly. Hence, considerable stress may be exerted on the mounting pads 33 due to temperature variation, possibly damaging the mounting pads 33 and their connections, thereby causing a disconnection.
Another problem is that a special resin layer (e.g., such as rubber or the like) is required for bonding, thereby requiring an additional manufacturing step and resulting in a more complex manufacturing method and device.